The invention herein relates to a hand held pipette which can be used for transferring different volumes of liquid without the need for changing the volumetric capillary tube portion of the pipette assembly. More particularly, the multi-volume displacement pipette herein is a disposable capillary or tubular tip assembly and corresponding plunger assembly which can be mounted on reusable plunger actuation assemblies to transfer various volumes of liquid. The multi-volume displacement pipette also includes disposable pipette tips which can be removably mounted on the liquid dispensing end of the pipette assembly for controlling the volume of liquid to be transferred.
Laboratory techniques frequently require repetitious handling of very small samples of liquids, for example, in the range from 1 to 250 microliters. In many instances varying volumes of the same liquid is transferred. Various pipetting devices are commercially available to simplify these otherwise laborious pipetting procedures. Some of the pipetting devices are described in the prior patent art including U.S. Pats. Nos. 3,606,086; 3,815,790; 3,827,305; 3,918,308; 4,054,062; and 4,084,730.
Another commercially available pipetting device includes a disposable, integral capillary and plunger tip assembly wherein the plunger tip is collet attached to an adjustable plunger stroking mechanism carried in the pipette handle to which the capillary is separately attached. Such an assembly is described in co-pending patent application Ser. No. 588,921, titled "Hand-Held Pipette With Disposable Capillary," filed Mar. 12, 1984, now U.S. Pat. No. 4,567,780, and assigned to the same assignee as the present application and for which the entire disclosure thereof is incorporated herein by this reference. The pipette assembly described therein has a common body or handle which houses the volumetric stroking mechanism, control and display. The assembly includes a set of disposable capillary tip assemblies for a wide range of volume and a body extender providing an interface between the disposable tip assembly and body or handle. The pipette assembly is easily separated into its parts for autoclaving or for exchange of body extenders having different functions such as so-called repettor or air displacement or positive displacement functions.
It would be desirable to provide a pipette asembly which can accommodate the transfer of varying volumes of liquid without the need for replacing the capillary bore volumetric tube portion of the pipette assembly.